diff --git a/internal/llm/llm.go b/internal/llm/llm.go
new file mode 100644
index 0000000..49b6ff9
--- /dev/null
+++ b/internal/llm/llm.go
@@ -0,0 +1,11 @@
+package llm
+
+import (
+	"context"
+	"somegit.dev/vikingowl/reddit-reader/internal/domain"
+)
+
+type Summarizer interface {
+	Score(ctx context.Context, post domain.Post, interests domain.Interests) (float64, error)
+	Summarize(ctx context.Context, post domain.Post) (string, error)
+}
diff --git a/internal/llm/openai.go b/internal/llm/openai.go
new file mode 100644
index 0000000..9e1db16
--- /dev/null
+++ b/internal/llm/openai.go
@@ -0,0 +1,145 @@
+package llm
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"strconv"
+	"strings"
+
+	"somegit.dev/vikingowl/reddit-reader/internal/domain"
+)
+
+type chatRequest struct {
+	Model       string        `json:"model"`
+	Messages    []chatMessage `json:"messages"`
+	Temperature float64       `json:"temperature"`
+}
+
+type chatMessage struct {
+	Role    string `json:"role"`
+	Content string `json:"content"`
+}
+
+type chatResponse struct {
+	Choices []struct {
+		Message struct {
+			Content string `json:"content"`
+		} `json:"message"`
+	} `json:"choices"`
+}
+
+// OpenAIClient speaks the OpenAI-compatible /v1/chat/completions API.
+// Works with Ollama, llama.cpp, and any other compatible backend.
+type OpenAIClient struct {
+	baseURL string
+	model   string
+	client  *http.Client
+}
+
+func NewOpenAIClient(baseURL, model string) *OpenAIClient {
+	return &OpenAIClient{
+		baseURL: baseURL,
+		model:   model,
+		client:  &http.Client{},
+	}
+}
+
+func (c *OpenAIClient) Score(ctx context.Context, post domain.Post, interests domain.Interests) (float64, error) {
+	system := buildScorePrompt(interests)
+	user := fmt.Sprintf("Title: %s\n\n%s", post.Title, truncate(post.SelfText, 500))
+
+	content, err := c.complete(ctx, system, user, 0.1)
+	if err != nil {
+		return 0, err
+	}
+
+	score, err := strconv.ParseFloat(strings.TrimSpace(content), 64)
+	if err != nil {
+		return 0, fmt.Errorf("llm: non-numeric score response %q: %w", content, err)
+	}
+	return score, nil
+}
+
+func (c *OpenAIClient) Summarize(ctx context.Context, post domain.Post) (string, error) {
+	system := "You are a concise summarizer. Produce exactly 5 bullet points summarizing the post. Each bullet starts with '- '."
+	user := fmt.Sprintf("Title: %s\n\n%s", post.Title, truncate(post.SelfText, 500))
+
+	return c.complete(ctx, system, user, 0.3)
+}
+
+func (c *OpenAIClient) complete(ctx context.Context, system, user string, temperature float64) (string, error) {
+	req := chatRequest{
+		Model: c.model,
+		Messages: []chatMessage{
+			{Role: "system", Content: system},
+			{Role: "user", Content: user},
+		},
+		Temperature: temperature,
+	}
+
+	body, err := json.Marshal(req)
+	if err != nil {
+		return "", fmt.Errorf("llm: marshal request: %w", err)
+	}
+
+	httpReq, err := http.NewRequestWithContext(ctx, http.MethodPost, c.baseURL+"/v1/chat/completions", bytes.NewReader(body))
+	if err != nil {
+		return "", fmt.Errorf("llm: build request: %w", err)
+	}
+	httpReq.Header.Set("Content-Type", "application/json")
+
+	resp, err := c.client.Do(httpReq)
+	if err != nil {
+		return "", fmt.Errorf("llm: http request: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return "", fmt.Errorf("llm: unexpected status %d", resp.StatusCode)
+	}
+
+	var chatResp chatResponse
+	if err := json.NewDecoder(resp.Body).Decode(&chatResp); err != nil {
+		return "", fmt.Errorf("llm: decode response: %w", err)
+	}
+	if len(chatResp.Choices) == 0 {
+		return "", fmt.Errorf("llm: no choices in response")
+	}
+
+	return chatResp.Choices[0].Message.Content, nil
+}
+
+// buildScorePrompt constructs the system prompt for relevance scoring.
+// Package-level so mistral.go can reuse it.
+func buildScorePrompt(interests domain.Interests) string {
+	var sb strings.Builder
+	sb.WriteString("You are a relevance scorer. Given a Reddit post and user interests, respond with a single float between 0.0 and 1.0 indicating relevance. No explanation, just the number.\n\n")
+	sb.WriteString("User interests: ")
+	sb.WriteString(interests.Description)
+
+	if len(interests.Examples) > 0 {
+		sb.WriteString("\n\nFeedback examples (post IDs the user rated):\n")
+		for _, ex := range interests.Examples {
+			vote := "interesting"
+			if ex.Vote < 0 {
+				vote = "not interesting"
+			}
+			fmt.Fprintf(&sb, "- %s: %s\n", ex.PostID, vote)
+		}
+	}
+
+	return sb.String()
+}
+
+// truncate shortens s to at most maxLen runes.
+// Package-level so mistral.go can reuse it.
+func truncate(s string, maxLen int) string {
+	runes := []rune(s)
+	if len(runes) <= maxLen {
+		return s
+	}
+	return string(runes[:maxLen])
+}
diff --git a/internal/llm/openai_test.go b/internal/llm/openai_test.go
new file mode 100644
index 0000000..4793527
--- /dev/null
+++ b/internal/llm/openai_test.go
@@ -0,0 +1,103 @@
+package llm_test
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"somegit.dev/vikingowl/reddit-reader/internal/domain"
+	"somegit.dev/vikingowl/reddit-reader/internal/llm"
+)
+
+func TestOpenAIScore(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/v1/chat/completions" {
+			t.Errorf("unexpected path: %s", r.URL.Path)
+		}
+		json.NewEncoder(w).Encode(map[string]any{
+			"choices": []map[string]any{
+				{"message": map[string]any{"role": "assistant", "content": "0.85"}},
+			},
+		})
+	}))
+	defer srv.Close()
+
+	client := llm.NewOpenAIClient(srv.URL, "test-model")
+	post := domain.Post{Title: "Go iterators", SelfText: "range over func patterns"}
+	interests := domain.Interests{Description: "Go programming"}
+
+	score, err := client.Score(context.Background(), post, interests)
+	if err != nil {
+		t.Fatalf("Score: %v", err)
+	}
+	if score != 0.85 {
+		t.Errorf("score = %f, want 0.85", score)
+	}
+}
+
+func TestOpenAISummarize(t *testing.T) {
+	want := "- point one\n- point two\n- point three\n- point four\n- point five"
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		json.NewEncoder(w).Encode(map[string]any{
+			"choices": []map[string]any{
+				{"message": map[string]any{"role": "assistant", "content": want}},
+			},
+		})
+	}))
+	defer srv.Close()
+
+	client := llm.NewOpenAIClient(srv.URL, "test-model")
+	got, err := client.Summarize(context.Background(), domain.Post{Title: "Test", SelfText: "Some content"})
+	if err != nil {
+		t.Fatalf("Summarize: %v", err)
+	}
+	if got != want {
+		t.Errorf("summary = %q, want %q", got, want)
+	}
+}
+
+func TestOpenAIScoreInvalidResponse(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		json.NewEncoder(w).Encode(map[string]any{
+			"choices": []map[string]any{
+				{"message": map[string]any{"role": "assistant", "content": "not a number"}},
+			},
+		})
+	}))
+	defer srv.Close()
+
+	client := llm.NewOpenAIClient(srv.URL, "test-model")
+	_, err := client.Score(context.Background(), domain.Post{Title: "Test"}, domain.Interests{})
+	if err == nil {
+		t.Error("expected error for non-numeric score response")
+	}
+}
+
+func TestOpenAIScorePromptIncludesFeedback(t *testing.T) {
+	var receivedBody map[string]any
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		json.NewDecoder(r.Body).Decode(&receivedBody)
+		json.NewEncoder(w).Encode(map[string]any{
+			"choices": []map[string]any{
+				{"message": map[string]any{"role": "assistant", "content": "0.5"}},
+			},
+		})
+	}))
+	defer srv.Close()
+
+	client := llm.NewOpenAIClient(srv.URL, "test-model")
+	interests := domain.Interests{
+		Description: "Go",
+		Examples:    []domain.Feedback{{PostID: "t3_good", Vote: 1}},
+	}
+	client.Score(context.Background(), domain.Post{Title: "Test"}, interests)
+
+	msgs := receivedBody["messages"].([]any)
+	systemMsg := msgs[0].(map[string]any)["content"].(string)
+	if !strings.Contains(systemMsg, "t3_good") {
+		t.Error("system prompt should contain feedback post IDs")
+	}
+}