V2 Bedrock: sessions silently die mid-turn (opus 5.5 and fable 5.1 confirmed)

[asaf-agami-cyera]

Description

The maxTokens value is omitted, so Bedrock defaults to 4096. In Claude Code the value is 128,000 for Opus 5.5, and 64.000 for Fable 5.1.

When Claude models think for more than 4k tokens, the turn ends without any answer, error or retry. Usually in the middle of a thinking block.

A workaround is to add this to opencode.jsonc:

  "providers": {
    "amazon-bedrock": {
      "models": {
        "global.anthropic.claude-fable-5-1": {
          "body": {
            "inferenceConfig": {
              "maxTokens": 64000,
            },
          },
        },
        "global.anthropic.claude-opus-5-5": {
          "body": {
            "inferenceConfig": {
              "maxTokens": 128000,
            },
          },
        },
      },
    },
  },

• Confirmed with Fable 5.1 and Opus 5.5, could be more models through Bedrock.
• Only tested in V2

Plugins

No response

OpenCode version

No response

Steps to reproduce

No response

Screenshot and/or share link

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Operating System

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Terminal

No response

[rekram1-node]

yeah it has to do with max tokens fixing today

[opencode-agent]

Fix merged into v2 in #51271. It landed after v2.0.18 and will be included in the next V2 release, v2.0.19. The output-token limit is now supplied to Bedrock Converse requests, preventing the omitted-maxTokens 4,096-token default described here.