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fix(opencode): Error 400 missing reasoning_content – transform reasoning according to DeepSeek API and aditional test cases #17529

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fix(opencode): Error 400 missing reasoning_content – transform reasoning according to DeepSeek API and aditional test cases #17529

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e2e25ab
transform to DeepSeek API fix and aditional test cases
Mar 10, 2026
2d8055d
fix: DeepSeek API thinking mode handling
Mar 9, 2026
cb163a1
chore: add clarifying comment for DeepSeek thinking mode fix
Mar 15, 2026
98e234d
Merge branch 'dev' into min
dixoxib Mar 15, 2026
bf33480
Merge branch 'dev' into min
dixoxib Mar 16, 2026
0d76fdc
Merge branch 'dev' into min
dixoxib Mar 16, 2026
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19 changes: 16 additions & 3 deletions packages/opencode/src/provider/transform.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -135,7 +135,17 @@ export namespace ProviderTransform {

if (typeof model.capabilities.interleaved === "object" && model.capabilities.interleaved.field) {
const field = model.capabilities.interleaved.field
return msgs.map((msg) => {
const isDeepSeek = model.providerID === "deepseek" || model.api.url?.includes("api.deepseek.com")
// Check if thinking mode is enabled for DeepSeek
const thinking = options.thinking as any
const isThinkingEnabled =
isDeepSeek &&
(model.capabilities.reasoning ||
model.api.id === "deepseek-reasoner" ||
model.id.includes("deepseek-reasoner") ||
(thinking && thinking.type === "enabled"))
const lastUserIndex = isThinkingEnabled ? msgs.findLastIndex((msg) => msg.role === "user") : -1
return msgs.map((msg, index) => {
if (msg.role === "assistant" && Array.isArray(msg.content)) {
const reasoningParts = msg.content.filter((part: any) => part.type === "reasoning")
const reasoningText = reasoningParts.map((part: any) => part.text).join("")
Expand All @@ -144,15 +154,16 @@ export namespace ProviderTransform {
const filteredContent = msg.content.filter((part: any) => part.type !== "reasoning")

// Include reasoning_content | reasoning_details directly on the message for all assistant messages
if (reasoningText) {
const shouldIncludeReasoning = reasoningText || (isThinkingEnabled && index > lastUserIndex)
if (shouldIncludeReasoning) {
return {
...msg,
content: filteredContent,
providerOptions: {
...msg.providerOptions,
openaiCompatible: {
...(msg.providerOptions as any)?.openaiCompatible,
[field]: reasoningText,
[field]: reasoningText || "",
},
},
}
Expand Down Expand Up @@ -1009,4 +1020,6 @@ export namespace ProviderTransform {

return schema as JSONSchema7
}

// DeepSeek thinking mode fix: ensures empty reasoning_content for assistant messages after last user message
}
240 changes: 238 additions & 2 deletions packages/opencode/test/provider/transform.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -773,7 +773,7 @@ describe("ProviderTransform.message - DeepSeek reasoning content", () => {
options: {},
headers: {},
release_date: "2023-04-01",
},
} as any,
{},
)

Expand All @@ -789,6 +789,72 @@ describe("ProviderTransform.message - DeepSeek reasoning content", () => {
expect(result[0].providerOptions?.openaiCompatible?.reasoning_content).toBe("Let me think about this...")
})

test("DeepSeek sets empty reasoning_content for assistant messages after last user message", () => {
const msgs = [
{
role: "user",
content: "First question",
},
{
role: "assistant",
content: [{ type: "text", text: "First answer" }],
},
{
role: "user",
content: "Second question",
},
{
role: "assistant",
content: [{ type: "text", text: "Second answer" }],
},
] as any[]

const result = ProviderTransform.message(
msgs,
{
id: "deepseek/deepseek-chat",
providerID: "deepseek",
api: {
id: "deepseek-chat",
url: "https://api.deepseek.com",
npm: "@ai-sdk/openai-compatible",
},
name: "DeepSeek Chat",
capabilities: {
temperature: true,
reasoning: true,
attachment: false,
toolcall: true,
input: { text: true, audio: false, image: false, video: false, pdf: false },
output: { text: true, audio: false, image: false, video: false, pdf: false },
interleaved: {
field: "reasoning_content",
},
},
cost: {
input: 0.001,
output: 0.002,
cache: { read: 0.0001, write: 0.0002 },
},
limit: {
context: 128000,
output: 8192,
},
status: "active",
options: {},
headers: {},
release_date: "2023-04-01",
} as any,
{},
)

expect(result).toHaveLength(4)
// First assistant (before last user) should NOT have reasoning_content
expect(result[1].providerOptions?.openaiCompatible?.reasoning_content).toBeUndefined()
// Second assistant (after last user) should have empty reasoning_content
expect(result[3].providerOptions?.openaiCompatible?.reasoning_content).toBe("")
})

test("Non-DeepSeek providers leave reasoning content unchanged", () => {
const msgs = [
{
Expand Down Expand Up @@ -833,7 +899,7 @@ describe("ProviderTransform.message - DeepSeek reasoning content", () => {
options: {},
headers: {},
release_date: "2023-04-01",
},
} as any,
{},
)

Expand All @@ -843,6 +909,176 @@ describe("ProviderTransform.message - DeepSeek reasoning content", () => {
])
expect(result[0].providerOptions?.openaiCompatible?.reasoning_content).toBeUndefined()
})

test("DeepSeek with reasoner model ID sets empty reasoning_content", () => {
const msgs = [
{
role: "user",
content: "Question",
},
{
role: "assistant",
content: [{ type: "text", text: "Answer" }],
},
] as any[]

const result = ProviderTransform.message(
msgs,
{
id: "deepseek/deepseek-reasoner",
providerID: "deepseek",
api: {
id: "deepseek-reasoner",
url: "https://api.deepseek.com",
npm: "@ai-sdk/openai-compatible",
},
name: "DeepSeek Reasoner",
capabilities: {
temperature: true,
reasoning: false, // reasoning false but model is reasoner
attachment: false,
toolcall: true,
input: { text: true, audio: false, image: false, video: false, pdf: false },
output: { text: true, audio: false, image: false, video: false, pdf: false },
interleaved: {
field: "reasoning_content",
},
},
cost: {
input: 0.001,
output: 0.002,
cache: { read: 0.0001, write: 0.0002 },
},
limit: {
context: 128000,
output: 8192,
},
status: "active",
options: {},
headers: {},
release_date: "2023-04-01",
} as any,
{},
)

expect(result).toHaveLength(2)
// Assistant after last user should have empty reasoning_content
expect(result[1].providerOptions?.openaiCompatible?.reasoning_content).toBe("")
})

test("DeepSeek with thinking option enabled sets empty reasoning_content", () => {
const msgs = [
{
role: "user",
content: "Question",
},
{
role: "assistant",
content: [{ type: "text", text: "Answer" }],
},
] as any[]

const result = ProviderTransform.message(
msgs,
{
id: "deepseek/deepseek-chat",
providerID: "deepseek",
api: {
id: "deepseek-chat",
url: "https://api.deepseek.com",
npm: "@ai-sdk/openai-compatible",
},
name: "DeepSeek Chat",
capabilities: {
temperature: true,
reasoning: false, // reasoning false
attachment: false,
toolcall: true,
input: { text: true, audio: false, image: false, video: false, pdf: false },
output: { text: true, audio: false, image: false, video: false, pdf: false },
interleaved: {
field: "reasoning_content",
},
},
cost: {
input: 0.001,
output: 0.002,
cache: { read: 0.0001, write: 0.0002 },
},
limit: {
context: 128000,
output: 8192,
},
status: "active",
options: {},
headers: {},
release_date: "2023-04-01",
} as any,
{
thinking: { type: "enabled" },
},
)

expect(result).toHaveLength(2)
// Assistant after last user should have empty reasoning_content
expect(result[1].providerOptions?.openaiCompatible?.reasoning_content).toBe("")
})

test("DeepSeek without thinking mode does not set empty reasoning_content", () => {
const msgs = [
{
role: "user",
content: "Question",
},
{
role: "assistant",
content: [{ type: "text", text: "Answer" }],
},
] as any[]

const result = ProviderTransform.message(
msgs,
{
id: "deepseek/deepseek-chat",
providerID: "deepseek",
api: {
id: "deepseek-chat",
url: "https://api.deepseek.com",
npm: "@ai-sdk/openai-compatible",
},
name: "DeepSeek Chat",
capabilities: {
temperature: true,
reasoning: false, // reasoning false
attachment: false,
toolcall: true,
input: { text: true, audio: false, image: false, video: false, pdf: false },
output: { text: true, audio: false, image: false, video: false, pdf: false },
interleaved: {
field: "reasoning_content",
},
},
cost: {
input: 0.001,
output: 0.002,
cache: { read: 0.0001, write: 0.0002 },
},
limit: {
context: 128000,
output: 8192,
},
status: "active",
options: {},
headers: {},
release_date: "2023-04-01",
} as any,
{}, // no thinking option
)

expect(result).toHaveLength(2)
// Assistant should NOT have reasoning_content because thinking mode not enabled
expect(result[1].providerOptions?.openaiCompatible?.reasoning_content).toBeUndefined()
})
})

describe("ProviderTransform.message - empty image handling", () => {
Expand Down
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