diff --git a/apps/api/internal/runner/candidate_platform_filter.go b/apps/api/internal/runner/candidate_platform_filter.go
new file mode 100644
index 0000000..a67e73a
--- /dev/null
+++ b/apps/api/internal/runner/candidate_platform_filter.go
@@ -0,0 +1,49 @@
+package runner
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/easyai/easyai-ai-gateway/apps/api/internal/store"
+)
+
+func filterCandidatesByRequestedPlatform(
+	candidates []store.RuntimeModelCandidate,
+	body map[string]any,
+) ([]store.RuntimeModelCandidate, error) {
+	platformID := firstNonEmptyString(
+		stringFromAny(body["platform_id"]),
+		stringFromAny(body["platformId"]),
+	)
+	platformModelID := firstNonEmptyString(
+		stringFromAny(body["platform_model_id"]),
+		stringFromAny(body["platformModelId"]),
+	)
+	if platformID == "" && platformModelID == "" {
+		return candidates, nil
+	}
+
+	filtered := make([]store.RuntimeModelCandidate, 0, len(candidates))
+	for _, candidate := range candidates {
+		if platformID != "" && !strings.EqualFold(candidate.PlatformID, platformID) {
+			continue
+		}
+		if platformModelID != "" && !strings.EqualFold(candidate.PlatformModelID, platformModelID) {
+			continue
+		}
+		filtered = append(filtered, candidate)
+	}
+	if len(filtered) > 0 {
+		return filtered, nil
+	}
+
+	requested := platformID
+	if platformModelID != "" {
+		requested = platformModelID
+	}
+	return nil, fmt.Errorf(
+		"%w: requested platform %q is unavailable for this model",
+		store.ErrNoModelCandidate,
+		requested,
+	)
+}
diff --git a/apps/api/internal/runner/candidate_platform_filter_test.go b/apps/api/internal/runner/candidate_platform_filter_test.go
new file mode 100644
index 0000000..2c2405f
--- /dev/null
+++ b/apps/api/internal/runner/candidate_platform_filter_test.go
@@ -0,0 +1,49 @@
+package runner
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/easyai/easyai-ai-gateway/apps/api/internal/store"
+)
+
+func TestFilterCandidatesByRequestedPlatform(t *testing.T) {
+	candidates := []store.RuntimeModelCandidate{
+		{PlatformID: "platform-a", PlatformModelID: "model-a"},
+		{PlatformID: "platform-b", PlatformModelID: "model-b"},
+	}
+
+	t.Run("without selection", func(t *testing.T) {
+		filtered, err := filterCandidatesByRequestedPlatform(candidates, map[string]any{})
+		if err != nil || len(filtered) != len(candidates) {
+			t.Fatalf("unexpected unfiltered candidates: %+v err=%v", filtered, err)
+		}
+	})
+
+	t.Run("snake case platform id", func(t *testing.T) {
+		filtered, err := filterCandidatesByRequestedPlatform(candidates, map[string]any{
+			"platform_id": "platform-b",
+		})
+		if err != nil || len(filtered) != 1 || filtered[0].PlatformID != "platform-b" {
+			t.Fatalf("unexpected platform filter result: %+v err=%v", filtered, err)
+		}
+	})
+
+	t.Run("camel case platform model id", func(t *testing.T) {
+		filtered, err := filterCandidatesByRequestedPlatform(candidates, map[string]any{
+			"platformModelId": "model-a",
+		})
+		if err != nil || len(filtered) != 1 || filtered[0].PlatformModelID != "model-a" {
+			t.Fatalf("unexpected platform model filter result: %+v err=%v", filtered, err)
+		}
+	})
+
+	t.Run("selection must be accessible and enabled", func(t *testing.T) {
+		filtered, err := filterCandidatesByRequestedPlatform(candidates, map[string]any{
+			"platformId": "platform-missing",
+		})
+		if len(filtered) != 0 || !errors.Is(err, store.ErrNoModelCandidate) {
+			t.Fatalf("unexpected unavailable platform result: %+v err=%v", filtered, err)
+		}
+	})
+}
diff --git a/apps/api/internal/runner/pricing.go b/apps/api/internal/runner/pricing.go
index 724acec..6bb6ef3 100644
--- a/apps/api/internal/runner/pricing.go
+++ b/apps/api/internal/runner/pricing.go
@@ -31,6 +31,10 @@ func (s *Service) Estimate(ctx context.Context, kind string, model string, body
 	if err != nil {
 		return EstimateResult{}, err
 	}
+	candidates, err = filterCandidatesByRequestedPlatform(candidates, body)
+	if err != nil {
+		return EstimateResult{}, err
+	}
 	candidates, _, err = filterRuntimeCandidatesByRequest(kind, model, modelType, body, candidates)
 	if err != nil {
 		return EstimateResult{}, err
diff --git a/apps/api/internal/runner/service.go b/apps/api/internal/runner/service.go
index 0c1e3bb..3eb931d 100644
--- a/apps/api/internal/runner/service.go
+++ b/apps/api/internal/runner/service.go
@@ -222,6 +222,9 @@ func (s *Service) executeWithToken(ctx context.Context, task store.GatewayTask,
 		CacheAffinityKeys:   cacheAffinityKeys.Lookup,
 		CacheAffinityPolicy: runnerPolicy.CacheAffinityPolicy,
 	})
+	if err == nil {
+		candidates, err = filterCandidatesByRequestedPlatform(candidates, body)
+	}
 	if err != nil {
 		if task.Kind == "responses" && responseExecution.PreviousChain != nil {
 			err = responseChainUnavailableError()