DeepSeek (AI SDK) requests use temperature=0 due to getModelParams defaultTemperature=0 shadowing DEEP_SEEK_DEFAULT_TEMPERATURE

[hannesrudolph]

Summary

When using the DeepSeek provider (AI SDK path), the outgoing request body shows temperature: 0 even though the intended DeepSeek default is DEEP_SEEK_DEFAULT_TEMPERATURE = 0.3.

Root Cause

• getModelParams() has a default parameter defaultTemperature = 0 (model-params.ts).
• DeepSeekHandler.getModel() calls getModelParams({ format: "openai", ... }) without passing defaultTemperature, so the computed temperature becomes 0 via:
  • customTemperature ?? model.defaultTemperature ?? defaultTemperature (model-params.ts)
  • which resolves to undefined ?? undefined ?? 0 => 0.
• The DeepSeek AI SDK request options then use:
  • temperature: this.options.modelTemperature ?? temperature ?? DEEP_SEEK_DEFAULT_TEMPERATURE (deepseek.ts)
  • Since temperature is 0 (not nullish), it wins and DEEP_SEEK_DEFAULT_TEMPERATURE is never reached.

Expected

If the user did not configure a temperature, DeepSeek requests should default to 0.3 as per DEEP_SEEK_DEFAULT_TEMPERATURE.

Actual

DeepSeek AI SDK requests default to 0 unless the user explicitly sets a temperature.

Suggested Fix (pick one)

Option A (targeted; minimal blast radius)

Pass defaultTemperature: DEEP_SEEK_DEFAULT_TEMPERATURE into getModelParams from DeepSeekHandler.getModel().

Option B (broader behavior change)

Change getModelParams default from 0 to undefined and update call sites/tests.

Option C (explicit defaults)

Change getModelParams default to undefined, then make each provider pass an explicit defaultTemperature matching its intended behavior.

Notes

This was discovered while fixing DeepSeek reasoning round-tripping; not part of that patch scope.

[roomote]

I've analyzed this issue and here's my proposed implementation plan:

Approach: Option A (targeted fix with minimal blast radius)

1. Modify src/api/providers/deepseek.ts line 46 to pass defaultTemperature: DEEP_SEEK_DEFAULT_TEMPERATURE to getModelParams():

const params = getModelParams({ 
  format: "openai", 
  modelId: id, 
  model: info, 
  settings: this.options,
  defaultTemperature: DEEP_SEEK_DEFAULT_TEMPERATURE  // Add this
})

2. The DEEP_SEEK_DEFAULT_TEMPERATURE constant (value 0.3) is already imported from @roo-code/types on line 5, so no additional imports are needed.

Why this works:

• Currently, getModelParams() uses defaultTemperature = 0 as its default parameter
• The temperature resolution chain is: customTemperature ?? model.defaultTemperature ?? defaultTemperature
• Since DeepSeek models don't have defaultTemperature set in their ModelInfo, the resolution falls through to the defaultTemperature parameter, which is 0
• By passing defaultTemperature: DEEP_SEEK_DEFAULT_TEMPERATURE, the resolution will correctly use 0.3 when no user-configured temperature exists

Benefits:

• Minimal code change (single line addition)
• No changes to getModelParams() signature or behavior for other providers
• Uses the existing DEEP_SEEK_DEFAULT_TEMPERATURE constant as intended
• The existing fallback on lines 124 and 164 (temperature ?? DEEP_SEEK_DEFAULT_TEMPERATURE) serves as an additional safety net

Please mention @roomote in a comment saying that you approve this plan, and I'll proceed with the implementation.