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fix(anthropic): support for claude mythos and fable models #3474

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Merged
amitksingh1490 merged 2 commits into from
Jun 10, 2026
+22 −1
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fix(anthropic): support for claude mythos and fable models #3474

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756f88b
feat(anthropic): add support for claude mythos and fable models
ssddOnTop Jun 9, 2026
3a460bd
Merge branch 'main' into feat/support-mythos-cc
ssddOnTop Jun 10, 2026
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7 changes: 7 additions & 0 deletions crates/forge_app/src/dto/anthropic/response.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -34,6 +34,8 @@ impl From<Model> for forge_domain::Model {
|| value.id.contains("claude-sonnet")
|| value.id.contains("claude-opus")
|| value.id.contains("claude-haiku")
|| value.id.contains("claude-mythos")
|| value.id.contains("claude-fable")
{
vec![
forge_domain::InputModality::Text,
Expand Down Expand Up @@ -77,6 +79,11 @@ impl From<Model> for forge_domain::Model {
/// header
/// - Legacy models may have different context lengths
fn get_context_length(model_id: &str) -> Option<u64> {
// Claude Mythos / Fable models (1M context)
if model_id.starts_with("claude-mythos") || model_id.starts_with("claude-fable") {
return Some(1_000_000);
}

// Current models (200K context)
if model_id.starts_with("claude-sonnet-4-5-")
|| model_id.starts_with("claude-haiku-4-5-")
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2 changes: 2 additions & 0 deletions crates/forge_app/src/transformers/model_specific_reasoning.rs
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Expand Up @@ -31,6 +31,8 @@ impl ModelSpecificReasoning {
|| id.contains("48-opus")
|| id.contains("opus-4-7")
|| id.contains("47-opus")
|| id.contains("mythos")
|| id.contains("fable")
{
// Opus 4.8 shares Opus 4.7's API contract: adaptive thinking only
// (legacy `budget_tokens` returns 400) and non-default sampling
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4 changes: 3 additions & 1 deletion crates/forge_repo/src/provider/anthropic.rs
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Expand Up @@ -101,7 +101,9 @@ fn interleaved_thinking_required(model: Option<&ModelId>) -> bool {
!(id.contains("opus-4-8")
|| id.contains("opus-4-7")
|| id.contains("opus-4-6")
|| id.contains("sonnet-4-6"))
|| id.contains("sonnet-4-6")
|| id.contains("mythos")
|| id.contains("fable"))
}

impl<T: HttpInfra> Anthropic<T> {
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10 changes: 10 additions & 0 deletions crates/forge_repo/src/provider/provider.json
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Expand Up @@ -634,6 +634,16 @@
"response_type": "Anthropic",
"url": "https://api.anthropic.com/v1/messages",
"models": [
{
"id": "claude-fable-5",
"name": "Claude Fable 5",
"description": "Most capable widely released model for demanding reasoning and agentic work",
"context_length": 1000000,
"tools_supported": true,
"supports_parallel_tool_calls": true,
"supports_reasoning": true,
"input_modalities": ["text", "image"]
},
{
"id": "claude-opus-4-8",
"name": "Claude Opus 4.8",
Expand Down
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