Gran Tierra stockholders are being asked to consider and vote to approve, among other matters, a proposal to approve the Share Purchase Agreement and the transactions contemplated thereby, including the Sale.On August 5, 2026, Seller entered into the Share Purchase Agreement pursuant to which, among other things, Seller will sell all of the issued and outstanding equity interests of the Company to Purchaser for the Consideration (which includes, among other things, cash, the assumption of debt and a pre-payment facility and the GTECI Note, and is subject to adjustment as described in the Share Purchase Agreement) and otherwise upon and subject to the terms and conditions set forth in the Share Purchase Agreement. We are seeking the approval of the Sale Proposal by our stockholders in accordance with Section 271 of the DGCL on the basis that the Sale may be considered to constitute the sale of substantially all of Gran Tierra’s property and assets within the meaning of that statute and related case law. The Board has unanimously approved the Share Purchase Agreement and the transactions contemplated thereby, including the Sale, and recommended that Gran Tierra’s stockholders approve the Share Purchase Agreement and the transactions contemplated thereby, including the Sale. A copy of the Share Purchase Agreement is attached to this Proxy Statement as Annex A.

We are seeking the approval of the Sale Proposal by our stockholders in accordance with Section 271 of the DGCL on the basis that the Sale may be considered to constitute the sale of substantially all of Gran Tierra’s property and assets within the meaning of that statute and related case law. Completion is conditioned on, among other things, Gran Tierra obtaining the Sale Required Stockholder Approval at the Special Meeting. Gran Tierra is sending these materials to you to help you decide how to vote your shares of Common Stock with respect to the Sale Proposal, the Compensation Proposal and the Adjournment Proposal to be considered at the Special Meeting. This Proxy Statement contains important information about the Special Meeting, the Sale Proposal, the Compensation Proposal and the Adjournment Proposal, and you should read it carefully.

In the course of reaching its decision to approve the Share Purchase Agreement and the transactions contemplated thereby, including the Sale, the Board considered a number of factors, including, among other things, the purchase price to be paid by Purchaser, the terms and conditions of the Share Purchase Agreement, the Sale, and the other transactions contemplated thereby, the financial condition and results of operations of Gran Tierra, the strategic and financial benefits to Gran Tierra that are expected to result from the Sale, and the prospects for the Retained Business. For additional information, see the section of this Proxy Statement entitled “Proposal No. 1—The Sale Proposal—Recommendation of the Gran Tierra Board of Directors and Its Reasons for the Sale” beginning on page 38.

Gran Tierra intends to use the net proceeds from the Sale to, among other things, substantially eliminate its remaining outstanding debt and to make strategic investments in Canada and Azerbaijan. The Board intends to work with its financial advisors to determine the best use of the remaining proceeds to increase stockholder value while continuing to evaluate strategic alternatives.For a description of how the proceeds from the Sale will be utilized, see the section of this Proxy Statement entitled “Proposal No. 1—The Sale Proposal — Use of Proceeds” beginning on page 40 and “Risk Factors—Risks Related to Gran Tierra Following Completion of the Sale” beginning on page 24.

Pursuant to the Sale, Purchaser will acquire complete equity ownership of the Company and its subsidiaries and related assets. The Sale will have no effect on the number of shares or the attributes of shares of Common Stock held by Gran Tierra’s stockholders. However, Gran Tierra’s business will undergo significant changes in connection with the Sale. As of immediately following Completion, Gran Tierra will no longer operate the Business. Gran Tierra will continue to operate the Retained Business, consisting of its interests in Canada and Azerbaijan. At this time, it is contemplated that, immediately following Completion, Gran Tierra will maintain the same corporate functions and the same senior executives and directors as Gran Tierra had prior to the completion of the Sale.

Yes. You should carefully review the section of this Proxy Statement entitled “Risk Factors” beginning on page 21, which presents risks and uncertainties related to the Sale and the operations of the Retained Business by Gran Tierra following the completion of the Sale or in the event the Share Purchase Agreement is terminated prior to completion of the Sale.

Your vote is very important. As a condition to the Completion of the Sale, Gran Tierra’s stockholders must approve the Sale Proposal, which requires the affirmative vote of the holders of a majority of the outstanding shares of Common Stock entitled to vote thereon at the Special Meeting, in person or by proxy.In addition to the approval of the Sale Proposal by Gran Tierra’s stockholders, each of the other conditions to the Completion of the Sale contained in the Share Purchase Agreement must be satisfied or waived. For additional information, see the section of this Proxy Statement entitled “The Share Sale and Purchase Agreement — Conditions to Completion of the Sale” beginning on page 65.

Yes. In addition to the Sale Proposal, Gran Tierra is also asking its stockholders to approve the Compensation Proposal, which is an advisory (non-binding) vote to approve certain compensation that may be payable to our named executive officers in connection with the Sale. Gran Tierra is also asking its stockholders to approve the Adjournment Proposal, which would authorize the adjournment of the Special Meeting, if necessary or appropriate, in order to solicit additional proxies if there are insufficient votes at the time of the Special Meeting to approve the Sale Proposal. Approval of each of the Compensation Proposal and the Adjournment Proposal requires the affirmative vote of the majority of the shares of Common Stock present virtually or represented by proxy at the Special Meeting and entitled to vote thereon.

We expect Completion of the Sale to occur in the second half of 2026 or first half of 2027, following the satisfaction or waiver of the last of the conditions to Completion (including receipt of the Sale Required Stockholder Approval).

The Board recommends that the Gran Tierra stockholders vote “FOR” the Sale Proposal, “FOR” the Compensation Proposal and “FOR” the Adjournment Proposal.

The proposed Sale is entirely a corporate action undertaken by Gran Tierra and its subsidiaries. Our stockholders will not realize any direct taxable gain or loss on their shares of Common Stock for U.S. federal income tax purposes as a result of the Sale. We do not anticipate that the Sale or the other transactions contemplated by the Share Purchase Agreement will result in any U.S. federal income tax consequences to our stockholders.Stockholders should refer to the discussion in the section of this Proxy Statement entitled “Proposal No. 1—The Sale Proposal—Material U.S. Federal Income Tax Consequences of the Sale” beginning on page 55 and the section of this Proxy Statement entitled “Unaudited Pro Forma Consolidated Financial Information” beginning on page 69.

No. No appraisal or dissenters’ rights are available to our stockholders under Delaware law or our Certificate of Incorporation or Bylaws in connection with the Sale or any other transactions contemplated by the Share Purchase Agreement, regardless of whether such stockholders vote for or against the approval of the Sale Proposal .

The Special Meeting will be held on October 9, 2026 at 10:00 a.m., Mountain Time, and will be held solely by remote communication, in a virtual-only format, or at such other time, on such other date and at such other place to which the Special Meeting may be adjourned.Instruction to Attend the Online MeetingLog in online at https://meetings.lumiconnect.com/400-691-155-645. The Meeting ID is 400-691-155-645. We recommend that you log in 15 minutes before the meeting starts.Enter the control number found on the form of proxy or notice, as applicable, into the stockholder login section.Enter the password: grantierraspIf you are a proxyholder, enter the credentials provided by Odyssey Trust CompanyIf you are a guest, complete the Guest login information.

Holders of Common Stock as of the close of business on September 14, 2026, the record date for the Special Meeting, are entitled to notice of, and to attend and vote at, the Special Meeting. Each share of Common Stock is entitled to one vote on all matters that come before the Special Meeting. As of the record date, there were 35,380,429 shares of Common Stock issued and outstanding .

Gran Tierra urges you to read this entire Proxy Statement carefully, including its annexes, and to consider how the Sale as contemplated by the Share Purchase Agreement and the actions contemplated by each of the Proposals may affect you.  If you are a stockholder of record, you may vote electronically at the Special Meeting, vote by proxy on the internet or vote by proxy using a proxy card that you may request or that we may elect to deliver at a later time. Whether or not you plan to attend the Special Meeting, we urge you to vote by proxy to ensure your vote is counted. You may still attend the Special Meeting and vote electronically even if you have already voted by proxy.To vote electronically during the Special Meeting, once you have logged into the meeting, you will be able to vote your shares electronically by clicking on the “Cast Your Vote” link on the meeting center site. It is important that you remain connected to the internet at all times during the Special Meeting in order to vote when balloting commences. It is your responsibility to ensure connectivity for the duration of the Special Meeting.To vote using the proxy card, simply complete, sign and date the proxy card that may be delivered and return it promptly in the envelope provided. If you return your signed proxy card to us by 10:00 a.m. Mountain Time on October 8, 2026, we will vote your shares as you direct.To vote on the internet, go to https://vote.odysseytrust.com and follow the on-screen instructions. You will need the control number located on the notice or in this Proxy Statement to access the voting site. Your internet vote must be received by 10:00 a.m. Mountain Time on October 8, 2026, to be counted. The Chair of the Special Meeting reserves the right to accept late proxies and may waive or extend the proxy cut-off, with or without notice, but is under no obligation to accept or reject any particular late proxy.We provide the option for internet proxy voting to allow you to vote your shares, with procedures designed to ensure the authenticity and correctness of your proxy vote instructions. However, please be aware that you must bear any costs associated with your internet access, such as usage charges from internet access providers.If you are a beneficial owner of shares registered in the name of your broker, bank, or other agent, you should have received proxy materials from that organization rather than from Gran Tierra. Simply follow the voting instructions you receive from your broker, bank, or other agent to ensure that your vote is counted. If you have received these proxy materials and voting instructions therein, simply complete and mail the voting instructions to ensure that your vote is counted. Alternatively, if permitted by your broker, bank, or other agent, you may vote by telephone or on the internet as instructed by your broker, bank or other agent. To vote electronically during the Special Meeting, you must obtain a valid proxy from your broker, bank, or other agent and appoint yourself as a proxyholder. Follow the instructions from your broker, bank, or other agent included with these proxy materials, or contact your broker, bank, or other agent to request a proxy form. In addition you must also register your appointment (of your broker or other agent) by emailing appointee@odysseytrust.com no later than the voting deadline and provide Odyssey with your name, email, number of shares appointed and name of your broker or other agent where shares are held, so that Odyssey may email the appointee their control number.

If you fail to return your proxy card or vote your shares through the Internet or if you hold shares in “street name” and you fail to instruct your broker, bank, or other agent how to vote, and do not vote electronically at the Special Meeting, your shares will not be counted for purposes of determining whether a quorum is present at the Special Meeting and, assuming the presence of a quorum, which is required to transact business at the Special Meeting, will have the same effect as an “AGAINST” vote with respect to the Sale Proposal, but will have no effect on the approval of the Compensation Proposal or the Adjournment Proposal.If you are a stockholder of record and you sign, date, and mail your proxy card without indicating how you wish to vote, all of your shares will be voted “FOR” the Sale Proposal, the Compensation Proposal and the Adjournment Proposal.  Whether or not you plan to attend the Special Meeting, we urge you to vote by proxy to ensure your vote is counted. You may still attend the Special Meeting and vote electronically even if you have already voted by proxy.

If you attend the Special Meeting or submit a proxy card, but affirmatively elect to abstain from voting, your proxy will be counted as present for the purpose of determining the presence of a quorum for the Special Meeting but will not be voted at the Special Meeting. As a result, your abstention will have the same effect as voting “AGAINST” the Sale Proposal, the Compensation Proposal and the Adjournment Proposal.

Broker non-votes relate to shares held in “street name” through brokers, banks, and other agents. If your shares are held in “street name” through an account with a broker, bank, or other agent, such broker, bank, or other agent is required to vote your shares according to your instructions, if provided. If you do not provide specific voting instructions, under the New York Stock Exchange (“NYSE”) rules governing banks and brokers who submit a proxy card with respect to shares held in “street name,” such banks and brokers have the discretionary authority to vote on routine matters, but not on non-routine matters. All of the proposals currently expected to be voted on at the Special Meeting are considered non-routine matters. A broker non-vote occurs when a bank or broker has not received voting instructions from the beneficial owner of the shares and the bank or broker cannot vote the shares in its discretion because the matter is not considered a routine matter under NYSE rules. Broker non-votes will have the same effect as voting “AGAINST” the Sale Proposal but will have no effect on the outcome of the vote for the Compensation Proposal or the Adjournment Proposal so long as a quorum is present.

As the beneficial owner, you are also invited to attend the Special Meeting. However, since a beneficial owner is not the stockholder of record, to vote electronically during the Special Meeting, you must obtain a valid proxy from your broker, bank, or other agent and appoint yourself as a proxyholder. Follow the instructions from your broker, bank, or other agent included with these proxy materials, or contact your broker, bank, or other agent to request a proxy form. In addition you must also register your appointment (of your broker, bank, or other agent) by emailing appointee@odysseytrust.com no later than the voting deadline and provide Odyssey with your name, email, number of shares appointed and name of your broker, bank, or other agent where shares are held, so that Odyssey may email the appointee their control number.Additionally, a stockholder has the right to appoint a person or entity (who need not be a stockholder) to attend and act for him/her on his/her behalf at the meeting other than the persons named in the enclosed instrument of Proxy. Stockholders who wish to appoint a third party proxyholder to represent them at the online Special Meeting must submit their proxy or voting instruction form (if applicable) prior to registering your proxyholder. Registering your proxyholder is an additional step once you have submitted your proxy or voting instruction form. Failure to register the proxyholder will result in the proxyholder not receiving a username to participate in the Special Meeting. To register a proxyholder, stockholders MUST email appointee@odysseytrust.com and provide Odyssey Trust Company with their proxyholder’s contact information, including email address of appointee, amount of shares appointed and the name of broker or other agent where shares are held, so that Odyssey Trust Company may provide the proxyholder with a control number via email. Requests for registration must be received by Odyssey Trust Company no later than 10:00 a.m. Mountain Time, on October 8, 2026. You will receive a confirmation of your registration by email after Odyssey Trust Company receives your registration materials. At the time of the meeting, go to https://meetings.lumiconnect.com/400-691-155-645. and enter your control number and the meeting password, grantierrasp

Yes. If you are a stockholder of record, you may revoke your proxy and change your vote at any time before your proxy is voted at the Special Meeting by returning a later-dated proxy card, by voting again over the Internet or electronically at the Special Meeting as more fully detailed in your proxy card, or by delivering written instructions to us at the principal executive offices of Gran Tierra before the Special Meeting. Attendance at the Special Meeting will not in and of itself cause your previously voted proxy to be revoked unless you specifically so request or vote again at the Special Meeting. If your shares are held in street name, you may change your vote by submitting new voting instructions to your broker, bank, or other agent, or, if you have obtained a valid proxy from your broker, bank, or other agent giving you the right to vote your shares, by attending the Special Meeting and voting electronically. If you have instructed your broker, bank, or other agent to vote your shares, you must follow directions received from your broker, bank, or other agent in order to change those instructions.

Shares of Common Stock that represent at least one-third of the total number of votes which may be cast by all holders of Common Stock, represented in person or by proxy, will constitute a quorum for the transaction of business at the Special Meeting. Your shares will be counted towards the quorum if you submit a valid proxy (or one is submitted on your behalf by your broker, bank, or other agent) or if you vote electronically at the Special Meeting. Shares of Common Stock held by stockholders in “street name” through a broker, bank, or other agent that do not instruct the agent how to vote such shares will not be counted for purposes of determining whether a quorum is present at the Special Meeting.

The Board is soliciting your proxy, and Gran Tierra will bear the cost of this solicitation of proxies. This includes the charges and expenses for preparation and distribution of this Proxy Statement and the related proxy materials. Kingsdale Advisors (“Kingsdale”), the strategic stockholder advisor and proxy solicitation agent, has been retained to assist Gran Tierra in the solicitation of proxies for the Special Meeting, and Gran Tierra will pay Kingsdale a fee estimated not to exceed CAD $250,000, plus reimbursement for its reasonable out-of-pocket expenses, and indemnify Kingsdale and its affiliates against certain claims, liabilities, losses, damages, and expenses for its services as Gran Tierra’s proxy solicitor.Gran Tierra will ask brokers, banks, and other agents holding shares of Common Stock beneficially owned by others to forward this Proxy Statement and the related proxy materials to their principals and to obtain their authority to execute proxies and voting instructions. Gran Tierra will reimburse such brokers, banks, and other agents for their reasonable out-of-pocket expenses for forwarding this Proxy Statement and the related proxy materials to Gran Tierra’s stockholders.

If you received more than one proxy card, your shares are likely registered in more than one name or are held in more than one account. Each proxy card you receive should be completed indicating how you wish to vote and returned separately in the postage-paid envelopes provided in order to ensure that all of your shares of Common Stock are voted.

No. The proceeds from the Sale will be paid directly to Gran Tierra, not Gran Tierra stockholders.

No. The Sale will not change the number of shares of Common Stock that you own or the rights associated with those shares. Following Completion, Gran Tierra will continue as a public company, but its business will be significantly different and will consist of the Retained Business.

If the Sale Proposal is not approved by the required vote of Gran Tierra stockholders, the Sale will not be completed unless the Share Purchase Agreement is amended or the parties otherwise determine to proceed in a manner permitted by applicable law and the terms of the Share Purchase Agreement. In that event, Gran Tierra would continue to own the Company and its subsidiaries unless and until another transaction is completed, and Gran Tierra may incur transaction-related costs without receiving the anticipated benefits of the Sale.

If there are insufficient votes at the time of the Special Meeting to approve the Sale Proposal, Gran Tierra may seek approval of the Adjournment Proposal to adjourn the Special Meeting to a later date or dates in order to solicit additional proxies. Gran Tierra may incur additional costs in connection with any such adjournment and related solicitation efforts.

Your prompt vote is important because approval of the Sale Proposal requires the affirmative vote of holders of a majority of the outstanding shares of Common Stock entitled to vote thereon, not merely a majority of the votes cast. As a result, a failure to vote, an abstention or a broker non-vote will have the same effect as a vote “AGAINST” the Sale Proposal. Voting promptly may also help Gran Tierra avoid the need for additional solicitation efforts or adjournments.

If you have questions about the proposals, this Proxy Statement, the Sale, the Special Meeting, or voting, or if you require other information related to the proxy solicitation, please contact Kingsdale, Gran Tierra’s strategic stockholder advisor and proxy solicitation agent, by calling 1-855-476-7987 (toll-free within North America) or 437-561-5013 (call or text) or by emailing contactus@kingsdaleadvisors.com. If you would like additional copies of this Proxy Statement or need to obtain proxy cards, please contact shareholders@odysseytrust.com. For additional information regarding the Special Meeting, including detailed voting instructions, key dates, other important information for stockholders, and to submit your vote please visit https://www.grantierra.com/events/special-meeting-of-shareholders/. If your shares are held through an account with a broker, bank, or other agent, you should call your broker, bank, or other agent for additional information.