fix(zen): 1M context window beta not sent for Opus 4.6 and Sonnet 4.5 #12452

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1. github-actions

   assigned

   fwang

   on Feb 6, 2026
2. github-actions

   added

   zenRelates to ZenRelates to Zen

   on Feb 6, 2026
3. github-actions commented on Feb 6, 2026

   

   github-actionsBot

   on Feb 6, 2026 – with GitHub Actions

   Contributor

   More actions

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

   • Claude Opus 4.6 context window limits still 200k #12438: Claude Opus 4.6 context window limits still 200k
   • 1M tokens for Opus 4.6 #12338: 1M tokens for Opus 4.6
   • [FEATURE]: support anthropic beta 1m token on bedrock #11267: [FEATURE]: support anthropic beta 1m token on bedrock
   • anthropic sonnet 4.5 1million token #2886: anthropic sonnet 4.5 1million token

   Feel free to ignore if none of these address your specific case.
4. nabilfreeman commented on Mar 23, 2026

   

   nabilfreeman

   on Mar 23, 2026

   Contributor

   More actions

   @ruslan-kurchenko

   ✅ Confirmed Working Solution for Sonnet 4.5 on Amazon Bedrock

   Successfully enabled 1M context for Claude Sonnet 4.5 on Amazon Bedrock using a config-only approach. No plugins needed.

   Configuration

   Add this to your opencode.json:

   {
     "provider": {
       "amazon-bedrock": {
         "models": {
           "global.anthropic.claude-sonnet-4-5-20250929-v1:0": {
             "limit": {
               "context": 1000000,
               "output": 64000
             },
             "options": {
               "anthropicBeta": ["context-1m-2025-08-07"]
             }
           }
         }
       }
     }
   }

   Key Points

   1. anthropicBeta option: Gets translated to additionalModelRequestFields.anthropic_beta in the Bedrock Converse API (not an HTTP header)
   2. limit.context: 1000000: Tells OpenCode about the 1M capacity, preventing premature auto-compaction (~968K instead of ~168K)
   3. Model-specific: Only affects Sonnet 4.5, doesn't impact other models

   Tested & Working

   • ✅ Tested on Amazon Bedrock (us-east-1)
   • ✅ Confirmed 1M context window is active
   • ✅ Auto-compaction triggers at correct threshold
   • ✅ Works with global inference profiles (global.anthropic.*)

   Hope this helps! 🎉
5. rekram1-node

   closed this as not plannedon May 1, 2026