subagent model variants are parsed but not applied at runtime in v1.4.0 #21632

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1. haitaoxw

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   bugSomething isn't workingSomething isn't working

   on Apr 9, 2026
2. github-actions

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   rekram1-node

   on Apr 9, 2026
3. github-actions

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   coreAnything pertaining to core functionality of the application (opencode server stuff)Anything pertaining to core functionality of the application (opencode server stuff)

   on Apr 9, 2026
4. github-actions commented on Apr 9, 2026

   

   github-actionsBot

   on Apr 9, 2026 – with GitHub Actions

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   This issue doesn't fully meet our contributing guidelines.

   What needs to be fixed:

   • OpenCode version is empty (_No response_) — please specify the exact version (e.g., v1.4.0)
   • Steps to reproduce is empty (_No response_) — please provide a minimal, reproducible sequence of steps so maintainers can verify the regression
   • Operating System and Terminal are also empty — environment info helps narrow down platform-specific issues

   Please edit this issue to address the above within 2 hours, or it will be automatically closed.

   ---

   This issue might be a duplicate of or related to existing issues. Please check:

   • Error when trying to use custom primary agent (TypeError: undefined is not an object (evaluating 'agent.variant')) #13790: Similar agent.variant bug where variant is parsed but not correctly applied at runtime for custom agents

   If you believe this was flagged incorrectly, please let a maintainer know.
5. github-actions

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   needs:complianceThis means the issue will auto-close after 2 hours.This means the issue will auto-close after 2 hours.

   and removed

   needs:complianceThis means the issue will auto-close after 2 hours.This means the issue will auto-close after 2 hours.

   on Apr 9, 2026
6. github-actions commented on Apr 9, 2026

   

   github-actionsBot

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   Thanks for updating the issue! It now follows the contributing guidelines and includes all the required information. We appreciate the detailed reproduction steps and version context.
7. nilltadios commented on Apr 17, 2026

   

   nilltadios

   on Apr 17, 2026

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   The bug reported here (a subagent's configured variant not applied at runtime) has a second, closely-related manifestation on the same code path: when a subagent has no configured model and inherits the parent's model, it also does not inherit the parent's active variant. The subagent ends up with variant = undefined and falls back to the provider default.

   Concrete symptom: a parent running gpt-5.4 at variant xhigh spawns a subagent that silently runs at reasoningEffort: "medium" (the default injected in provider/transform.ts around line 871–883 for gpt-5.4 when no variant is present). The subagent "thinks" visibly less than the parent, which is what first tipped me off.

   Root cause trace (on current dev, 54078c4):

   1. packages/opencode/src/tool/task.ts:102-105 reads only modelID / providerID from the parent assistant message:

      const model = next.model ?? {
        modelID: msg.info.modelID,
        providerID: msg.info.providerID,
      }

      msg.info.variant exists on the assistant message schema (session/message-v2.ts:448) but is never read.

   2. task.ts:131-145 then calls ops.prompt({ ..., model: { modelID, providerID }, ... }) with no variant field.

   3. packages/opencode/src/session/prompt.ts:935-941 resolves variant as:

      const same = ag.model && model.providerID === ag.model.providerID && model.modelID === ag.model.modelID
      const full = !input.variant && ag.variant && same ? ... : undefined
      const variant = input.variant ?? (ag.variant && full?.variants?.[ag.variant] ? ag.variant : undefined)

      For an inherited-model subagent, ag.model is undefined → same is false → the ag.variant branch is gated off → variant is undefined.

   So there are two distinct failure modes routing through the same spot:

   • The one originally reported here: subagent has its own model + variant, but something in the v1.4.0 runtime path still drops it. (Guard on line 941 requiring full?.variants?.[ag.variant] is a likely suspect — if full fails to resolve for any reason, the variant is silently dropped.)
   • This extension: subagent inherits the parent's model and gets no variant at all, because the parent's variant is never forwarded through task.ts.

   Minimal fix for the second case: carry msg.info.variant through task.ts and pass it as input.variant to ops.prompt, so variant inheritance follows model inheritance. That alone should address the parent-inheritance symptom; the configured-variant-ignored path on line 941 likely needs a separate look.
8. 0serna commented on Apr 24, 2026

   

   0serna

   on Apr 24, 2026

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   same issue
9. 21pounder commented on Apr 29, 2026

   

   21pounder

   on Apr 29, 2026

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   I've investigated this bug and can confirm the root cause with debug logs.

   Root cause

   In packages/opencode/src/session/prompt.ts:902:

   const same = ag.model && model.providerID === ag.model.providerID && model.modelID === ag.model.modelID

   When a subagent has no explicit model configured (inheriting the parent's), ag.model is undefined → same is false → ag.variant is silently dropped.

   I added a temporary debug log to confirm:

   log.info("variant debug", { agVariant: ag.variant, inputVariant: input.variant, same, variant, agModel: ag.model })

   Subagent running (configured with variant: "high", no model):

   

   Bug confirmed — agVariant=high is present but variant is missing (undefined):

   

   Fix

   const same = !ag.model || (model.providerID === ag.model.providerID && model.modelID === ag.model.modelID)

   I'll open a PR with this one-line change.
10. thdxr

    removed

    bugSomething isn't workingSomething isn't working

    coreAnything pertaining to core functionality of the application (opencode server stuff)Anything pertaining to core functionality of the application (opencode server stuff)

    on May 3, 2026
11. thdxr

    assigned

    jlongster

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    rekram1-node

    on May 3, 2026
12. jsheremeta-alt commented on Jun 4, 2026

    

    jsheremeta-alt

    on Jun 4, 2026

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    Still reproducing on v1.15.13. Here is additional evidence from the runtime binary and local session database.

    Binary analysis

    The Task tool execute function resolves the model like this:

    let b = $.model ?? {modelID: I.info.modelID, providerID: I.info.providerID}

    Then passes only modelID and providerID to the prompt call:

    G.prompt({
      model: {modelID: b.modelID, providerID: b.providerID},
      agent: $.name,
      ...
    })

    No variant, no options, no reasoningEffort, no enable_thinking, no temperature. The prompt function does accept variant as a top-level parameter (the TUI path uses it this way), but the Task tool never passes it. This is the same root cause that @nilltadios and @21pounder traced above.

    Session database evidence

    I queried the OpenCode SQLite database (~/.local/share/opencode/opencode.db) to check what sub-agent sessions actually record at runtime:

    SELECT id, parent_id, agent, model, tokens_reasoning 
    FROM session 
    WHERE parent_id IS NOT NULL 
    ORDER BY time_updated DESC

    Every single sub-agent session has variant: "default" in the model field, regardless of what is configured in agent frontmatter. My build-steward sub-agent has enable_thinking: true, reasoningEffort: high in its frontmatter but recorded 0 reasoning tokens in its actual run. Other sub-agents show similarly mismatched token counts.

    Primary agents do apply variants correctly. Those sessions show the correct variant value.

    About the closed PRs

    PR #20742 by @dbpolito addressed this but was closed by automated PR cleanup on May 15 due to insufficient reactions. PR #12567 by @mugnimaestra has been open since February with a working fix and video demonstration but remains unmerged.

    Could #20742 be reopened? It had tests and was from an SST team member.

    👍React with 👍1Reacted by mariusg0000
13. github-actions commented on Aug 4, 2026

    

    github-actionsBot

    on Aug 4, 2026 – with GitHub Actions

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    To stay organized issues are automatically closed after 60 days of no activity. If the issue is still relevant please open a new one.

    👎React with 👎2Reacted by Atiab BZ and Yevhen D
14. github-actions

    closed this as not plannedon Aug 4, 2026