diff --git a/generators/ruby-v2/sdk/src/root-client/RootClientGenerator.ts b/generators/ruby-v2/sdk/src/root-client/RootClientGenerator.ts
index 23185be30cd8..78f065edab8f 100644
--- a/generators/ruby-v2/sdk/src/root-client/RootClientGenerator.ts
+++ b/generators/ruby-v2/sdk/src/root-client/RootClientGenerator.ts
@@ -56,10 +56,8 @@ export class RootClientGenerator extends FileGenerator<RubyFile, SdkCustomConfig
         });
         parameters.push(baseUrlParameter);
 
-        const authenticationParameter = this.getAuthenticationParameter();
-        if (authenticationParameter != null) {
-            parameters.push(authenticationParameter);
-        }
+        const authenticationParameters = this.getAuthenticationParameters();
+        parameters.push(...authenticationParameters);
 
         const method = ruby.method({
             name: "initialize",
@@ -92,11 +90,13 @@ export class RootClientGenerator extends FileGenerator<RubyFile, SdkCustomConfig
         return method;
     }
 
-    private getAuthenticationParameter(): ruby.KeywordParameter | undefined {
+    private getAuthenticationParameters(): ruby.KeywordParameter[] {
+        const parameters: ruby.KeywordParameter[] = [];
+
         for (const scheme of this.context.ir.auth.schemes) {
             switch (scheme.type) {
-                case "bearer":
-                    return ruby.parameters.keyword({
+                case "bearer": {
+                    const param = ruby.parameters.keyword({
                         name: TOKEN_PARAMETER_NAME,
                         type: ruby.Type.string(),
                         initializer:
@@ -107,12 +107,30 @@ export class RootClientGenerator extends FileGenerator<RubyFile, SdkCustomConfig
                                 : undefined,
                         docs: undefined
                     });
+                    parameters.push(param);
+                    break;
+                }
+                case "header": {
+                    const param = ruby.parameters.keyword({
+                        name: scheme.name.name.snakeCase.safeName,
+                        type: ruby.Type.string(),
+                        initializer:
+                            scheme.headerEnvVar != null
+                                ? ruby.codeblock((writer) => {
+                                      writer.write(`ENV.fetch("${scheme.headerEnvVar}", nil)`);
+                                  })
+                                : undefined,
+                        docs: undefined
+                    });
+                    parameters.push(param);
+                    break;
+                }
                 default:
-                    return undefined;
+                    break;
             }
         }
 
-        return undefined;
+        return parameters;
     }
 
     private getRawClientHeaders(): ruby.TypeLiteral {
@@ -138,6 +156,17 @@ export class RootClientGenerator extends FileGenerator<RubyFile, SdkCustomConfig
                         value: ruby.TypeLiteral.string(`Bearer #{${TOKEN_PARAMETER_NAME}}`)
                     });
                     break;
+                case "header": {
+                    const headerParamName = header.name.name.snakeCase.safeName;
+                    const headerName = header.name.wireValue;
+                    const headerValue =
+                        header.prefix != null ? `${header.prefix} #{${headerParamName}}` : `#{${headerParamName}}`;
+                    headers.push({
+                        key: ruby.TypeLiteral.string(headerName),
+                        value: ruby.TypeLiteral.string(headerValue)
+                    });
+                    break;
+                }
                 default:
                     break;
             }
diff --git a/generators/ruby-v2/sdk/versions.yml b/generators/ruby-v2/sdk/versions.yml
index 9464bd432786..266aa34d8350 100644
--- a/generators/ruby-v2/sdk/versions.yml
+++ b/generators/ruby-v2/sdk/versions.yml
@@ -1,5 +1,14 @@
 # yaml-language-server: $schema=../../../fern-versions-yml.schema.json
 
+- version: 1.0.0-rc29
+  createdAt: "2025-10-21"
+  changelogEntry:
+    - type: feat
+      summary: |
+        Add support for API key (header-based) authentication in Ruby SDK generator.
+        Supports multiple authentication schemes in the same API.
+  irVersion: 59
+
 - version: 1.0.0-rc28
   createdAt: "2025-10-01"
   changelogEntry:
diff --git a/seed/ruby-sdk-v2/any-auth/lib/seed/client.rb b/seed/ruby-sdk-v2/any-auth/lib/seed/client.rb
index 1711477e4ac1..1293bf2a343a 100644
--- a/seed/ruby-sdk-v2/any-auth/lib/seed/client.rb
+++ b/seed/ruby-sdk-v2/any-auth/lib/seed/client.rb
@@ -3,13 +3,14 @@
 module Seed
   class Client
     # @return [Seed::Client]
-    def initialize(base_url:, token: ENV.fetch("MY_TOKEN", nil))
+    def initialize(base_url:, token: ENV.fetch("MY_TOKEN", nil), api_key: ENV.fetch("MY_API_KEY", nil))
       @raw_client = Seed::Internal::Http::RawClient.new(
         base_url: base_url,
         headers: {
           "User-Agent": "fern_any-auth/0.0.1",
           "X-Fern-Language": "Ruby",
-          Authorization: "Bearer #{token}"
+          Authorization: "Bearer #{token}",
+          "X-API-Key": api_key.to_s
         }
       )
     end
diff --git a/seed/ruby-sdk-v2/custom-auth/lib/seed/client.rb b/seed/ruby-sdk-v2/custom-auth/lib/seed/client.rb
index 7c960490797e..e066ca2d4fe6 100644
--- a/seed/ruby-sdk-v2/custom-auth/lib/seed/client.rb
+++ b/seed/ruby-sdk-v2/custom-auth/lib/seed/client.rb
@@ -3,12 +3,13 @@
 module Seed
   class Client
     # @return [Seed::Client]
-    def initialize(base_url:)
+    def initialize(base_url:, custom_auth_scheme:)
       @raw_client = Seed::Internal::Http::RawClient.new(
         base_url: base_url,
         headers: {
           "User-Agent": "fern_custom-auth/0.0.1",
-          "X-Fern-Language": "Ruby"
+          "X-Fern-Language": "Ruby",
+          "X-API-KEY": custom_auth_scheme.to_s
         }
       )
     end