diff --git a/docs/enterprise-configuration.md b/docs/enterprise-configuration.md
new file mode 100644
index 0000000000..da05d6dfd8
--- /dev/null
+++ b/docs/enterprise-configuration.md
@@ -0,0 +1,236 @@
+# Custom API Endpoint Configuration
+
+This guide explains how to configure GitHub Agentic Workflows to use custom API endpoints for GitHub Enterprise Cloud (GHEC), GitHub Enterprise Server (GHES), or custom AI endpoints.
+
+## Overview
+
+GitHub Agentic Workflows supports custom API endpoints through the `engine.api-target` configuration field. This allows you to specify custom endpoints for:
+
+- **GitHub Enterprise Cloud (GHEC)** - Tenant-specific Copilot API endpoints
+- **GitHub Enterprise Server (GHES)** - Enterprise Copilot API endpoints
+- **Custom AI Endpoints** - Custom OpenAI-compatible or Anthropic-compatible endpoints
+
+## Configuration
+
+To configure a custom API endpoint, add the `api-target` field to your engine configuration:
+
+**Basic Configuration:**
+
+```yaml
+---
+engine:
+  id: copilot
+  api-target: api.acme.ghe.com
+network:
+  allowed:
+    - defaults
+    - acme.ghe.com
+    - api.acme.ghe.com
+---
+```
+
+The `api-target` field accepts a hostname (without protocol or path) and works with any agentic engine.
+
+## Examples
+
+### GitHub Enterprise Cloud (GHEC)
+
+For GHEC tenants (domains ending with `.ghe.com`), specify your tenant-specific API endpoint:
+
+**Workflow Configuration:**
+
+```yaml
+---
+engine:
+  id: copilot
+  api-target: api.acme.ghe.com
+network:
+  allowed:
+    - defaults
+    - acme.ghe.com
+    - api.acme.ghe.com
+---
+```
+
+**Required domains in network allowlist:**
+- `acme.ghe.com` - Your GHEC tenant domain (git operations, web UI)
+- `api.acme.ghe.com` - Your tenant-specific Copilot API endpoint
+- `raw.githubusercontent.com` - Raw content access (if using GitHub MCP server)
+
+### GitHub Enterprise Server (GHES)
+
+For GHES instances (custom domains), specify the enterprise Copilot endpoint:
+
+**Workflow Configuration:**
+
+```yaml
+---
+engine:
+  id: copilot
+  api-target: api.enterprise.githubcopilot.com
+network:
+  allowed:
+    - defaults
+    - github.company.com
+    - api.enterprise.githubcopilot.com
+---
+```
+
+**Required domains in network allowlist:**
+- `github.company.com` - Your GHES instance (git operations, web UI)
+- `api.enterprise.githubcopilot.com` - Enterprise Copilot API endpoint (used for all GHES instances)
+
+### Custom AI Endpoints
+
+The `api-target` field works with any agentic engine, allowing you to use custom AI endpoints:
+
+**Workflow Configuration:**
+
+```yaml
+---
+engine:
+  id: codex
+  api-target: api.custom.ai-provider.com
+network:
+  allowed:
+    - defaults
+    - api.custom.ai-provider.com
+---
+```
+
+## Complete Examples
+
+### GHEC with GitHub MCP Server
+
+```yaml
+---
+description: Workflow for GHEC environment with GitHub API access
+on:
+  workflow_dispatch:
+permissions:
+  contents: read
+  issues: write
+  pull-requests: write
+engine:
+  id: copilot
+  api-target: api.acme.ghe.com
+tools:
+  github:
+    mode: remote
+    toolsets: [default]
+network:
+  allowed:
+    - defaults
+    - acme.ghe.com
+    - api.acme.ghe.com
+    - raw.githubusercontent.com
+---
+
+# Your workflow prompt here
+```
+
+### GHES with Custom Endpoint
+
+```yaml
+---
+description: Workflow for GHES environment
+on:
+  issue_comment:
+    types: [created]
+permissions:
+  contents: read
+  issues: write
+engine:
+  id: copilot
+  api-target: api.enterprise.githubcopilot.com
+network:
+  allowed:
+    - defaults
+    - github.company.com
+    - api.enterprise.githubcopilot.com
+---
+
+# Your workflow prompt here
+```
+
+### Custom AI Provider
+
+```yaml
+---
+description: Workflow with custom AI endpoint
+on:
+  workflow_dispatch:
+permissions:
+  contents: read
+engine:
+  id: codex
+  api-target: api.custom.ai-provider.com
+network:
+  allowed:
+    - defaults
+    - api.custom.ai-provider.com
+---
+
+# Your workflow prompt here
+```
+
+## Verification
+
+To verify your configuration is working correctly:
+
+### 1. Check Compiled Workflow
+
+After compiling your workflow, check the generated `.lock.yml` file:
+
+```bash
+gh aw compile your-workflow.md
+```
+
+Look for:
+- `--copilot-api-target` flag in AWF command (if using Copilot engine)
+- Correct API endpoint hostname in the flag value
+
+### 2. Check Workflow Runs
+
+In GitHub Actions workflow runs:
+1. Go to the agent job
+2. Check the "Run Copilot Agent" (or equivalent) step
+3. Verify the AWF command includes the correct API target
+4. Check AWF logs for API connection messages
+
+## Troubleshooting
+
+### Wrong API Endpoint
+
+**Problem:** Traffic is going to the wrong API endpoint
+
+**Solutions:**
+1. Verify `engine.api-target` is set correctly in your workflow frontmatter
+2. Check that the domain is in your `network.allowed` list
+3. Review AWF logs in the workflow run for endpoint configuration messages
+4. Ensure you're not using a full URL (use hostname only: `api.acme.ghe.com` not `https://api.acme.ghe.com`)
+
+### Domain Not Whitelisted
+
+**Problem:** Requests are blocked with network errors
+
+**Solution:** Add the missing domain to your `network.allowed` list:
+- For GHEC: `[acme.ghe.com, api.acme.ghe.com]`
+- For GHES: `[github.company.com, api.enterprise.githubcopilot.com]`
+- For custom AI: `[api.custom.ai-provider.com]`
+
+### GitHub MCP Server Issues
+
+**Problem:** GitHub MCP server fails to connect to your enterprise instance
+
+**Solutions:**
+1. Ensure your GHEC/GHES domain is in `network.allowed`
+2. Verify the GitHub token has appropriate scopes for your enterprise tenant
+3. Use `mode: remote` for the GitHub MCP server when on GHEC/GHES
+
+## Related Documentation
+
+- [AWF Firewall Configuration](https://github.com/github/gh-aw-firewall) - Detailed AWF documentation
+- [GitHub Actions Environment Variables](https://docs.github.com/en/actions/learn-github-actions/variables#default-environment-variables) - Default GitHub Actions variables
+- [Network Permissions](network.md) - Network access configuration
+- [Tools Configuration](tools.md) - MCP server and tool setup
diff --git a/pkg/parser/schemas/main_workflow_schema.json b/pkg/parser/schemas/main_workflow_schema.json
index e331e1e95b..af31aac657 100644
--- a/pkg/parser/schemas/main_workflow_schema.json
+++ b/pkg/parser/schemas/main_workflow_schema.json
@@ -7971,6 +7971,11 @@
               "type": "string",
               "description": "Agent identifier to pass to copilot --agent flag (copilot engine only). Specifies which custom agent to use for the workflow."
             },
+            "api-target": {
+              "type": "string",
+              "description": "Custom API endpoint hostname for the agentic engine. Used for GitHub Enterprise Cloud (GHEC), GitHub Enterprise Server (GHES), or custom AI endpoints. Example: 'api.acme.ghe.com' for GHEC, 'api.enterprise.githubcopilot.com' for GHES, or custom endpoint hostnames.",
+              "examples": ["api.acme.ghe.com", "api.enterprise.githubcopilot.com", "api.custom.endpoint.com"]
+            },
             "args": {
               "type": "array",
               "items": {
diff --git a/pkg/workflow/awf_helpers.go b/pkg/workflow/awf_helpers.go
index fe84d182ab..b59525badc 100644
--- a/pkg/workflow/awf_helpers.go
+++ b/pkg/workflow/awf_helpers.go
@@ -205,6 +205,13 @@ func BuildAWFArgs(config AWFCommandConfig) []string {
 		awfHelpersLog.Printf("Added --anthropic-api-target=%s", anthropicTarget)
 	}
 
+	// Add Copilot API target for custom Copilot endpoints (GHEC, GHES, or custom)
+	// This uses the engine.api-target field if configured
+	if config.WorkflowData.EngineConfig != nil && config.WorkflowData.EngineConfig.APITarget != "" {
+		awfArgs = append(awfArgs, "--copilot-api-target", config.WorkflowData.EngineConfig.APITarget)
+		awfHelpersLog.Printf("Added --copilot-api-target=%s", config.WorkflowData.EngineConfig.APITarget)
+	}
+
 	// Add SSL Bump support for HTTPS content inspection (v0.9.0+)
 	sslBumpArgs := getSSLBumpArgs(firewallConfig)
 	awfArgs = append(awfArgs, sslBumpArgs...)
diff --git a/pkg/workflow/copilot_engine_execution.go b/pkg/workflow/copilot_engine_execution.go
index 184d8e854d..ceeeb0d406 100644
--- a/pkg/workflow/copilot_engine_execution.go
+++ b/pkg/workflow/copilot_engine_execution.go
@@ -259,6 +259,7 @@ COPILOT_CLI_INSTRUCTION="$(cat /tmp/gh-aw/aw-prompts/prompt.txt)"
 
 	// Always add GH_AW_PROMPT for agentic workflows
 	env["GH_AW_PROMPT"] = "/tmp/gh-aw/aw-prompts/prompt.txt"
+
 	// Tag the step as a GitHub AW agentic execution for discoverability by agents
 	env["GITHUB_AW"] = "true"
 	// Indicate the phase: "agent" for the main run, "detection" for threat detection
diff --git a/pkg/workflow/engine.go b/pkg/workflow/engine.go
index 0149a6cdfb..76955165d6 100644
--- a/pkg/workflow/engine.go
+++ b/pkg/workflow/engine.go
@@ -26,6 +26,7 @@ type EngineConfig struct {
 	Args             []string
 	Firewall         *FirewallConfig // AWF firewall configuration
 	Agent            string          // Agent identifier for copilot --agent flag (copilot engine only)
+	APITarget        string          // Custom API endpoint hostname (e.g., "api.acme.ghe.com" or "api.enterprise.githubcopilot.com")
 
 	// Inline definition fields (populated when engine.runtime is specified in frontmatter)
 	IsInlineDefinition bool   // true when the engine is defined inline via engine.runtime + optional engine.provider
@@ -314,6 +315,14 @@ func (c *Compiler) ExtractEngineConfig(frontmatter map[string]any) (string, *Eng
 				}
 			}
 
+			// Extract optional 'api-target' field (custom API endpoint for any engine)
+			if apiTarget, hasAPITarget := engineObj["api-target"]; hasAPITarget {
+				if apiTargetStr, ok := apiTarget.(string); ok && apiTargetStr != "" {
+					config.APITarget = apiTargetStr
+					engineLog.Printf("Extracted api-target: %s", apiTargetStr)
+				}
+			}
+
 			// Return the ID as the engineSetting for backwards compatibility
 			engineLog.Printf("Extracted engine configuration: ID=%s", config.ID)
 			return config.ID, config
diff --git a/pkg/workflow/engine_test.go b/pkg/workflow/engine_test.go
index 34e4ba7d5a..d8f65c5c83 100644
--- a/pkg/workflow/engine_test.go
+++ b/pkg/workflow/engine_test.go
@@ -250,3 +250,79 @@ func TestEngineCommandField(t *testing.T) {
 		})
 	}
 }
+
+// TestAPITargetExtraction tests that the api-target configuration is correctly
+// extracted from frontmatter for custom API endpoints (GHEC, GHES, or custom AI endpoints).
+func TestAPITargetExtraction(t *testing.T) {
+	tests := []struct {
+		name              string
+		frontmatter       map[string]any
+		expectedAPITarget string
+	}{
+		{
+			name: "GHEC api-target",
+			frontmatter: map[string]any{
+				"engine": map[string]any{
+					"id":         "copilot",
+					"api-target": "api.acme.ghe.com",
+				},
+			},
+			expectedAPITarget: "api.acme.ghe.com",
+		},
+		{
+			name: "GHES api-target",
+			frontmatter: map[string]any{
+				"engine": map[string]any{
+					"id":         "copilot",
+					"api-target": "api.enterprise.githubcopilot.com",
+				},
+			},
+			expectedAPITarget: "api.enterprise.githubcopilot.com",
+		},
+		{
+			name: "custom api-target",
+			frontmatter: map[string]any{
+				"engine": map[string]any{
+					"id":         "codex",
+					"api-target": "api.custom.endpoint.com",
+				},
+			},
+			expectedAPITarget: "api.custom.endpoint.com",
+		},
+		{
+			name: "no api-target",
+			frontmatter: map[string]any{
+				"engine": map[string]any{
+					"id": "copilot",
+				},
+			},
+			expectedAPITarget: "",
+		},
+		{
+			name: "empty api-target",
+			frontmatter: map[string]any{
+				"engine": map[string]any{
+					"id":         "copilot",
+					"api-target": "",
+				},
+			},
+			expectedAPITarget: "",
+		},
+	}
+
+	compiler := NewCompiler()
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			_, config := compiler.ExtractEngineConfig(tt.frontmatter)
+
+			if config == nil {
+				t.Fatal("Expected config to be non-nil")
+			}
+
+			if config.APITarget != tt.expectedAPITarget {
+				t.Errorf("Expected api-target %q, got %q", tt.expectedAPITarget, config.APITarget)
+			}
+		})
+	}
+}
diff --git a/pkg/workflow/secrets_validation.go b/pkg/workflow/secrets_validation.go
index 5e9e3dbc83..50aee2ad6b 100644
--- a/pkg/workflow/secrets_validation.go
+++ b/pkg/workflow/secrets_validation.go
@@ -12,9 +12,6 @@ var secretsValidationLog = newValidationLogger("secrets")
 // This is the same pattern used in the github_token schema definition ($defs/github_token).
 var secretsExpressionPattern = regexp.MustCompile(`^\$\{\{\s*secrets\.[A-Za-z_][A-Za-z0-9_]*(\s*\|\|\s*secrets\.[A-Za-z_][A-Za-z0-9_]*)*\s*\}\}$`)
 
-// secretNamePattern validates that a secret name follows environment variable naming conventions
-var secretNamePattern = regexp.MustCompile(`^[A-Z][A-Z0-9_]*$`)
-
 // validateSecretsExpression validates that a value is a proper GitHub Actions secrets expression.
 // Returns an error if the value is not in the format: ${{ secrets.NAME }} or ${{ secrets.NAME || secrets.NAME2 }}
 // Note: This function intentionally does not accept the secret key name as a parameter to prevent