Or, for Claude Mythos 5.1, which offers the same capabilities to verified organizations: changedmodels/fable-5-1/migration-guide
Nearest release: v2.1.302, published an hour after this site recorded the change. Shown because the two are within 24 hours of each other. Nothing here says the release caused the edit.
Recorded here
Lines+16added
Lines−12removed
From line
422
where the diff opens
First seen
1 Sep 2026
this site's first read of the page
Recorded edits25to this page, all time
The whole hunk
from line 422, old and new numbered
/
from line 422
422422
423423 var parameters = new MessageCreateParams
424424 {
425 Model = "claude-fable-5-1",
425 Model = Model.ClaudeFable5_1,
426426 MaxTokens = 16000,
427427 Tools = [
428428 new ToolUnion(new Tool()
from line 455
455455 client := anthropic.NewClient()
456456
457457 response, err := client.Messages.New(context.TODO(), anthropic.MessageNewParams{
458 Model: "claude-fable-5-1",
458 Model: anthropic.ModelClaudeFable5_1,
459459 MaxTokens: 16000,
460460 Tools: []anthropic.ToolUnionParam{
461461 {OfTool: &anthropic.ToolParam{
from line 490
490490 AnthropicClient client = AnthropicOkHttpClient.fromEnv();
491491
492492 MessageCreateParams params = MessageCreateParams.builder()
493 .model("claude-fable-5-1")
493 .model(Model.CLAUDE_FABLE_5_1)
494494 .maxTokens(16000L)
495495 .addTool(Tool.builder()
496496 .name("record_summary")
from line 725
725725
726726 var parameters = new MessageCreateParams
727727 {
728 Model = "claude-fable-5-1",
728 Model = Model.ClaudeFable5_1,
729729 MaxTokens = 16000,
730730 System = "You are a customer support assistant for an online electronics store.",
731731 Tools = [
from line 768
768768 client := anthropic.NewClient()
769769
770770 response, err := client.Messages.New(context.TODO(), anthropic.MessageNewParams{
771 Model: "claude-fable-5-1",
771 Model: anthropic.ModelClaudeFable5_1,
772772 MaxTokens: 16000,
773773 System: []anthropic.TextBlockParam{
774774 {Text: "You are a customer support assistant for an online electronics store."},
from line 816
816816 AnthropicClient client = AnthropicOkHttpClient.fromEnv();
817817
818818 MessageCreateParams params = MessageCreateParams.builder()
819 .model("claude-fable-5-1")
819 .model(Model.CLAUDE_FABLE_5_1)
820820 .maxTokens(16000L)
821821 .system("You are a customer support assistant for an online electronics store.")
822822 .addTool(Tool.builder()
from line 1030
10301030 ```csharp C#
10311031 using Anthropic.Models.Beta;
10321032 using Anthropic.Models.Beta.Messages;
1033 using Model = Anthropic.Models.Messages.Model;
10331034
10341035 AnthropicClient client = new();
10351036
from line 1037
10361037 var response = await client.Beta.Messages.Create(
10371038 new()
10381039 {
1039 Model = "claude-fable-5-1",
1040 Model = Model.ClaudeFable5_1,
10401041 MaxTokens = 16000,
10411042 Thinking = new BetaThinkingConfigAdaptive
10421043 {
from line 1073
10721073 client := anthropic.NewClient()
10731074
10741075 response, err := client.Beta.Messages.New(context.TODO(), anthropic.BetaMessageNewParams{
1075 Model: "claude-fable-5-1",
1076 Model: anthropic.ModelClaudeFable5_1,
10761077 MaxTokens: 16000,
10771078 Thinking: anthropic.BetaThinkingConfigParamUnion{
10781079 OfAdaptive: &anthropic.BetaThinkingConfigAdaptiveParam{
from line 1106
11051106 import com.anthropic.models.beta.messages.BetaThinkingConfigAdaptive;
11061107 import com.anthropic.models.beta.messages.BetaThinkingPrefixMismatchBehavior;
11071108 import com.anthropic.models.beta.messages.MessageCreateParams;
1109 import com.anthropic.models.messages.Model;
11081110
11091111 void main() {
11101112 AnthropicClient client = AnthropicOkHttpClient.fromEnv();
11111113
11121114 MessageCreateParams params = MessageCreateParams.builder()
1113 .model("claude-fable-5-1")
1115 .model(Model.CLAUDE_FABLE_5_1)
11141116 .maxTokens(16000L)
11151117 .addBeta(AnthropicBeta.THINKING_BINDING_CONTROLS_2026_08_01)
11161118 .thinking(BetaThinkingConfigAdaptive.builder()
from line 1338
13361338 ```csharp C#
13371339 using Anthropic.Models.Beta;
13381340 using Anthropic.Models.Beta.Messages;
1341 using Model = Anthropic.Models.Messages.Model;
13391342
13401343 AnthropicClient client = new();
13411344
13421345 var response = await client.Beta.Messages.Create(new MessageCreateParams
13431346 {
1344 Model = "claude-fable-5-1",
1347 Model = Model.ClaudeFable5_1,
13451348 MaxTokens = 4096,
13461349 OutputConfig = new() { Effort = Effort.High },
13471350 Messages =
from line 1376
13731376 client := anthropic.NewClient()
13741377
13751378 response, err := client.Beta.Messages.New(context.Background(), anthropic.BetaMessageNewParams{
1376 Model: "claude-fable-5-1",
1379 Model: anthropic.ModelClaudeFable5_1,
13771380 MaxTokens: 4096,
13781381 OutputConfig: anthropic.BetaOutputConfigParam{
13791382 Effort: anthropic.BetaOutputConfigEffortHigh,
from line 1413
14101413 import com.anthropic.models.beta.messages.BetaOutputConfig;
14111414 import com.anthropic.models.beta.messages.BetaSystemMessageOutputConfig;
14121415 import com.anthropic.models.beta.messages.MessageCreateParams;
1416 import com.anthropic.models.messages.Model;
14131417
14141418 void main() {
14151419 AnthropicClient client = AnthropicOkHttpClient.fromEnv();
14161420
14171421 MessageCreateParams params = MessageCreateParams.builder()
1418 .model("claude-fable-5-1")
1422 .model(Model.CLAUDE_FABLE_5_1)
14191423 .maxTokens(4096L)
14201424 .addBeta(AnthropicBeta.MID_CONVERSATION_OUTPUT_CONFIG_2026_07_01)
14211425 .outputConfig(BetaOutputConfig.builder()
No line in this hunk matches that.